Fix commission check for existing asset

This patch adds anchoring to the search expression used to detect
existing assets with the same FQDN. Without this assets with similar
names can cause incorrect detection of duplicate FQDNs.

For example:

existing asset: foo.example.com
new assets: bazfoo.example.com

The existing asset would cause a commission of bazfoo.example.com to
fail.
Merge pull request #8 from richardmarshall/master

Fix commission check for existing asset